Data Node Scan
Description
If the GUC parameter enable_fast_query_shipping is set to on, the optimizer attempts to push down the query statement from the CN to DNs for execution, and then returns the execution result to the DNs.
Typical Scenarios
Use query statements that can be pushed down.
Examples
Queries that can be pushed down
-- Prepare data. gaussdb=#SET enable_fast_query_shipping=on; gaussdb=#DROP TABLE IF EXISTS t1; gaussdb=#CREATE TABLE t1 (id int, number int, grade int); -- Execution result. gaussdb=#EXPLAIN SELECT * FROM t1 where id > 1; QUERY PLAN -------------------------------------------------- Data Node Scan (cost=0.00..0.00 rows=0 width=0) Node/s: All datanodes (2 rows)
The actual plan is generated on the DN. To view the execution plan on the DN, set the max_datanode_for_plan parameter.
-- Enable a parameter. gaussdb=#SET max_datanode_for_plan = 1; -- Execution result. gaussdb=#EXPLAIN SELECT * FROM t1 where id > 1; QUERY PLAN -------------------------------------------------------------------- Data Node Scan (cost=0.00..0.00 rows=0 width=0) Node/s: All datanodes Remote SQL: SELECT id, "number", grade FROM public.t1 WHERE id > 1 Datanode Name: datanode1 Seq Scan on t1 (cost=0.00..34.31 rows=648 width=12) Filter: (id > 1) (8 rows) -- Drop. gaussdb=#DROP TABLE IF EXISTS t1;
Item |
Description |
---|---|
Data Node Scan |
Specifies the operator name. |
Node/s: All datanodes |
Delivers data to all DNs. |
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